1. Field of the Invention
The present invention relates to automatic transmissions such as continuously variable transmissions for automotive vehicles.
2. Description of the Related Art
FIG. 4 shows a known continuously variable transmission for a motor vehicle. The known continuously variable transmission includes a stepping motor 1 having a reciprocating rod 16, a first link 100 connected to the reciprocating rod 16, a second link 101 connected to the first link 100, and a transmission control valve 102 connected to the second link 101 at an intermediate part thereof. The known continuously variable transmission also includes a first pulley 103 connected to the second link 101 at an end of the second link 101 and to an engine 107 via an engine shaft 106, a second pulley 105 connected to the first pulley 103 via a metallic belt 104 and to a wheel 109 via a driving shaft 108, and a hydraulic servo structure for driving the transmission control valve 102.
The hydraulic servo structure includes an oil pump 110, an oil pan 111, a controller 112 for controlling the transmission control valve 102 and the like so that the driving shaft 108 and the engine shaft 106 rotate at a predetermined ratio of rotational speeds between each other, and a speed sensor 113 for determining the rotation of the first pulley 103 and the second pulley 105, respectively.
A transmission structure for controlling the ratio of rotational speeds between the driving shaft 108 and the engine shaft 106 is formed with the first pulley 103, the second pulley 105, and the metallic belt 104.
In the continuously variable transmission, the rod 16 is reciprocated by the rotation of the stepping motor 1, thereby opening and closing the transmission control valve 102 via the first and second links 100 and 101, whereby an operating oil for the first pulley 103 is supplied and discharged through the transmission control valve 102. The second link 101 pivots on a supporting point A.
The operating oil from the transmission control valve 102 moves a drum 103a of the first pulley 103, thereby varying the ratio of the diameters between the first and second pulleys 103 and 105 on which the metallic belt 104 is mounted, and controlling the ratio of the rotational speeds of the driving shaft 108 and the engine shaft 106.
FIG. 5 is a plan view of the stepping motor 1 shown in FIG. 4. FIG. 6 is a sectional view of the stepping motor 1 shown in FIG. 5 along a line VIxe2x80x94VI. FIG. 7 is a sectional view of the stepping motor 1 shown in FIG. 6 along a line VIIxe2x80x94VII. FIG. 8 is a sectional view of the stepping motor 1 shown in FIG. 6 along a line VIIIxe2x80x94VIII. FIG. 9 is a perspective view of a critical portion of the stepping motor 1 shown in FIG. 4.
In the drawings, the permanent-magnet-type stepping motor 1 includes a resin casing 2, a resin cylindrical housing 12 connected with the casing 2, a motor body 3 housed in the casing 2, a shaft 4 to be rotated by the motor body 3, and a converting structure 31 for converting the rotational movement of the shaft 4 into linear movement. The cover is composed of the casing 2 and the housing 12.
The motor body 3 includes a stator 5 fixed to the casing 2, and a rotor 6 fixed to the shaft 4. The stator 5 includes a coil 7 having a conductor made of a copper wire covered with an insulative film which is wound in a plurality of turns, coil terminals 8 led out from the coil 7, connector terminals 9 connected to the coil terminals 8, and external terminals 25 connected to the connector terminals 9. The rotor 6 includes a bush 10 fixed to the shaft 4, and a hollow cylindrical permanent-magnet 11 fixed to the bush 10.
The housing 12 is fixed at a first end thereof to the casing 2 by a plurality of screws 12A extending parallel to the shaft 4. The casing 2 is provided with a circular mating hole 2a formed therein, and the housing 12 is provided with a mating member 12a so as to be inserted in the mating hole 2a. In FIG. 7, the mating member 12a is provided with three positioning-protrusions 12b at the outer periphery of the mating member 12a, the positioning protrusions 12b protruding in the radial directions and in contact with the inner periphery of the mating hole 2a. The housing 12 is provided with an annular groove 12c formed therein at a face in connection with the casing 2.
The housing 12 is provided therein with a housing through-hole 12d communicating between the outside and the inside of the housing 12, the housing through-hole 12d being provided at a side face of the housing 12. A filter 13 for capturing contamination of oil is provided in the housing through-hole 12d. The shaft 4 is rotatably supported by bearings 14 and 15. The bearing 15 affixed in the housing 15 is a rubber-seal-type bearing.
The housing 12 is provided, at a second end thereof opposite to the first end fixed to the casing 2, with a rod 16 which reciprocates along the axis of the shaft 4 with the rotation of the shaft 4. The rod 16 is inserted into the housing 12 at the base end of the rod 16, and the other end of the rod 16 protrudes from the second end of the housing 12. The rod 16 is provided therein with a through-hole 16a communicating between the inside of the housing 12 and the inside of the rod 16. The housing 12 is provided at the inner face of the second end thereof with a sleeve 17 for guiding the rod 16 linearly moving, an oil seal 18 for avoiding contamination to penetrate from the outer periphery of the rod 16, and an annular stopper 19 for restricting the linear movement of the rod 16.
The converting structure 31 includes a threaded part 4a of the shaft 4, a resin guide member 20 disposed at the base end of the rod 16 and coupled with the threaded part 4a, and a metallic stopper 21 for restricting the linear movement of the rod 16 at the other side of the annular stopper 19. The guide member 20 and the stopper 21 include stopper faces 20b and 21a, respectively, perpendicular to the rotational axis of the shaft 4. In FIG. 8, the guide member 20 is provided with rotation-restricting protrusions 20a for restricting rotation of the rod 16 formed extending in the radial directions at the outer periphery of the guide member 20. With this arrangement, the guide member 20 is moved in the axial direction of the shaft 4 by the rotation thereof. The rod 16 is mounted with a resin member 22 to be coupled with the first link 100 at the end opposite to the base end of the rod 16.
In the stepping motor 1 having the above-described configuration, when electrical current is applied to the coil 7 via the connectors 25, a rotation-driving magnetic field is generated in the coil 7, thereby rotating the rotor 6 and the shaft 4 as a unit. The shaft 4 is coupled with the guide member 20 at the threaded part 4a of the shaft 4, and the rotational movement of the guide member 20 is restricted, whereby the rotational movement of the shaft 4 is converted into the linear movement of the guide member 20 and the rod 16.
By the linear movement of the rod 16 in both directions, the transmission control valve 102 is opened and closed via the first and second links 100 and 101, whereby the ratio of rotational speeds between the driving shaft 108 and the engine shaft 106 varies, as described above.
In the known continuously variable transmission, the stepping motor 1 is dipped in oil containing sulfur and organic sulfur compounds. Therefore, sulfur and the like transmit through an insulative film of a conductor included in the coil 7, and a sulfur compound is produced so as to be disposed between a copper wire and the insulative film by the chemical reaction between the copper wire and the sulfur, whereby the adhesion between the insulative film and the copper wire is reduced. In this case, there is a risk in that the insulative film is damaged by friction of the adjacent copper wires with each other caused by repeated thermal expansion and contraction due to a thermal hysteresis of the copper wires, whereby copper dissolves due to the potential gradient between the adjacent copper wires, thereby causing short circuits or, sometimes disconnection. Particularly, the insulative film is more likely to be damaged at a position in which the conductor and a bobbin is in contact with each other which have thermal expansion coefficients differing from each other, whereby there is a greater risk of short circuits and disconnection.
Moreover, when the temperature in the oil is increased by the heat from the coil 7 to a level higher than the vaporization temperature of volatile components, sulfur and the like are more likely to transmit through the insulative film and to cause short circuits between the wires.
Accordingly, it is an object of the present invention to provide an automatic transmission including a motor in which the risk of short circuits and disconnection of conductors is significantly reduced.
To this end, according to a first aspect of the present invention, an automatic transmission comprises a transmission case containing oil; a transmission structure housed in the transmission case, for varying the ratio of rotational speeds between a driving shaft connected to wheels and an engine shaft connected to an engine; a transmission control valve housed in the transmission case, for controlling the transmission structure; and a motor as a driving source for driving the transmission control valve. The motor includes a cover, a motor body having a coil disposed under the cover and formed with a wound conductor, a shaft rotated by an electrical current applied to the coil, and a converting structure for converting the rotational movement of the shaft into linear movement. The motor is fixed to the transmission case so that the motor body is disposed in air.
A smaller case which houses the motor body therein may be provided in the transmission case so as to communicate with the air.
The cover may include a casing for housing the motor body and a housing connected to the casing, and a shoulder part of the housing may be in contact with the transmission case at the periphery of a connecting hole formed in the transmission case.
The cover may include a casing for housing the motor body and a housing connected to the casing, and a shoulder part of the housing may be in contact with the smaller case at the periphery of a connecting hole formed in the smaller case.
According to a second aspect of the present invention, an automatic transmission comprises a transmission case containing oil; a transmission structure housed in the transmission case, for varying the ratio of rotational speeds between a driving shaft connected to wheels and an engine shaft connected to an engine; a transmission control valve housed in the transmission case, for controlling the transmission structure; and a motor as a driving source for driving the transmission control valve. The motor includes a cover, a motor body having a coil disposed under the cover and formed with a wound conductor, a shaft rotated by an electrical current applied to the coil, a converting structure for converting the rotational movement of the shaft into linear movement, and a heat-releasing plate in contact with the motor body at the periphery thereof and provided with a corrugated part formed on a surface of the heat-releasing plate.
According to a third aspect of the present invention, an automatic transmission comprises a transmission case containing oil; a transmission structure housed in the transmission case, for varying the ratio of rotational speeds between a driving shaft connected to wheels and an engine shaft connected to an engine; a transmission control valve housed in the transmission case, for controlling the transmission structure; and a motor as a driving source for driving the transmission control valve. The motor includes a cover, a motor body having a coil disposed under the cover and formed with a wound conductor, a shaft rotated by an electrical current applied to the coil, and a converting structure for converting the rotational movement of the shaft into linear movement. The value of the electrical current applied to the coil and the number of winding turns of the conductor are set so that the temperature in the oil is below the vaporization temperature of the oil.
The motor may further include a heat-releasing plate in contact with the motor body at the periphery thereof and provided with a corrugated part formed on a surface of the heat-releasing plate.
The motor may be a stepping motor.